There has hitherto been known a multibranched polymer having a structure comprising a core moiety constituting a core and a lot of arm chains which is bonded with the core moiety.
As a method for producing such a multibranched polymer, for example,
(a) a method comprising the steps of converting AB type and ABA type block polymers each having a different amphiphilic property into micelles in a solvent, and crosslinking the micelles or crosslinking an inner core by some method (Japanese Unexamined Patent Publication No. 10-195152),(b) a method of forming an arm moiety from a core compound using a polymerization method such as living polymerization method (Macromol. Chem., 189, 2885-2889 (1998)), and(c) a method of utilizing a dendrimer having a lot of multibranched chains (Japanese Unexamined Patent Publication No. 6-219966) are known.
However, in the method (a) of utilizing a block polymer, micelles must be formed in a critical micell concentration and it may be difficult to form micelles according to the composition of a polymer, and also it may be difficult to internally crosslink even if micells are formed. In the method (b) of forming an arm from a core compound using a polymerization method, a high technique and polymerization equipments in the polymerization are required. In the method (c) of utilizing a dendrimer, although the dendrimer to be used is a compound having excellent multibranching properties, a high synthetic technique is required similarly to the method (b).
As the other multibranched polymer, a star polymer comprising a core made of benzene or porphyrin, and an arm made of polyethylene oxide is also known (Macromolecules, 32, 484-4793 (1999) and Angew. Chem. Int. Ed., (21), 3215-3218 (1999)). However, any core made of benzene or porphyrin has a planar and rigid structure and has such a drawback that mobility of a chain moiety of the star polymer is restricted.
Also, it is reported that a polymer having a star-shaped structure is obtained by polymerizing methyl methacrylate, isobutyl methacrylate and t-butyl methacrylate using, as a polymerization initiator, diphenylhexyl lithium obtained by reacting 1,1-diphenylethylene with sec-butyl lithium, and reacting with dicumyl alcohol dimethacrylate or 2,5-dimethyl-2,5-hexanediol dimethacrylate (J. Polymer Science, Part A, 3083 (2003)).
However, molecular weight distribution of the multibranched polymer obtained by conventional production methods including the above described methods is 1.5 or more and thus it was difficult to form a multibranched polymer comprising an arm having the same polymer chain length.
Therefore, it is required to develop a technique of producing a narrowly dispersed multibranched polymer having a controlled molecular structure, simply and efficiently.
As a polymer solid electrolyte, a polymer solid electrolyte containing a X—Y—X type triblock copolymer as a matrix base material, which is obtained by copolymerizing methoxypolyethylene glycol monomethacrylate (component X) with styrene (component Y) using a living anionic polymerization method, has hitherto been proposed (Macromol. Chem., 190, 1069 (1989)). In the matrix base material described in this document, the component X is a component which forms a PEO domain as diffusion transport space of lithium ions. Therefore, it is preferred to increase the content of the component X in the matrix base material so as to enhance ionic conductivity.
However, since a homopolymer of the methoxypolyethylene glycol monomethacrylate as the component X is a liquid material at room temperature even if converted into a high molecular weight compound, the content of the component X is limited so as to use the X—Y—X type copolymer as the above matrix base material of the solid electrolyte. This fact means that the shape and size of the PEO domain as the diffusion transport space of lithium ions are limited. Actually, ionic conductivity at 40° C. of the matrix base material was unsatisfactory as 10−6 S/cm.
Also, WO02/40594 proposes a polymer solid electrolyte having flexibility wherein a hydrogen bond of poly(ethylene glycol)bis(carboxymethyl)ether and a nitrogen-containing heterocyclic compound such as pyrazine is utilized.
However, in the polymer solid electrolyte described in this document, a hydrogen bond with a polymer having a hydrogen bond site at the end of the polymer is utilized, and a hydrogen bond with a hydrogen bondable functional group in a repeating unit in polymer main chain is not utilized. Also, the polymer solid electrolyte is not still put in practical use because of lower ionic conductivity than that of a poly(ethylene glycol)bis(carboxymethyl)ether element.
Furthermore, WO02/40594 discloses that, when an ionic conductive polymer having a hydrogen bondable functional group in a repeating unit in a polymer main chain or an ionic conductive cyclic compound having a hydrogen bondable functional group contains a compound wherein a hydrogen bond is formed with a low molecular compound having a hydrogen bond site, control of a chain structure of the polymer and ionic conductivity are improved. In the document, a compound having a hydroxyl group, a carboxyl group or an amino group is disclosed as a low molecular compound.
However, the polymer solid electrolyte described in this document didn't have characteristics which satisfy both ionic conductivity and shape stability.
Therefore, it has been required to develop a polymer solid electrolyte which has excellent thermal characteristics, excellent physical characteristics and ionic conductivity.